Protective anti-glucan antibodies with preference for beta-1,3- glucans

ABSTRACT

Anti-β-1,3-glucan antibodies have been found to be protective against systemic fungal infection with  Candida albicans . The present invention provides monoclonal antibodies that bind to β-1,3-glucan, hybridoma cell lines producing the antibodies, compositions comprising the antibodies and methods of using such antibodies for treatment of microbial infections, particularly against  Candida albicans  and  Aspergillus fumigatis  infections. The antibodies of the present invention are not specific for β-1,6-glucan.

All documents cited herein are incorporated by reference in theirentirety.

TECHNICAL FIELD

This invention relates to monoclonal antibodies and their use intherapy, particularly in the treatment of fungal infections and disease.

BACKGROUND ART

Fungal infections are prevalent in several clinical settings,particularly in immunocompromised patients. The emergence of resistanceto antimycotics, in particular to the azoles, has increased interest intherapeutic and prophylactic vaccination against these fingi [1]. Amongfungal pathogens, Candida albicans is one of the most prevalent. Thisorganism is one of the principal agents of widespread opportunisticinfections in humans and causes candidiasis, a condition which is foundin both normal and immunocompromised patients.

There is widespread consensus in the field of medical mycology thatcellular immunity is critical for successful host defence against fungi[2], although the potential efficacy of humoral immunity in protectingagainst two major fungal pathogens (C. albicans and C. neoformans) hasattracted attention [3]. For C. neoformans, antibodies to the capsularglucuronoxylomannan have been shown to mediate protection in animalmodels of infection. For C. albicans, cell-surface mannoproteins are thedominant antigenic components of C. albicans and antibodies to mannan,proteases and a heat shock proteins have been associated with protectionagainst infection. Other vaccine candidates include: members of theaspartyl proteinase (Sap2) family; the 65 kDa mannoprotein (MP65) [4];adhesion molecules isolated from phosphomannan cell wall complexes [5];peptides which mimic epitopes from the mannan portion of thephosphomannan complex of Candida [6]; and hemolysin-like proteins [7].

Glucans are glucose-containing polysaccharides found inter alia infungal cell walls. a-glucans include one or more a-linkages betweenglucose subunits and β-glucans include one or more β-linkages betweenglucose subunits. Within a typical fungal cell wall, β-1,3-glucanmicrofibrils are interwoven and crosslinked with chitin microfibrils toform the inner skeletal layer, whereas the outer layer consists ofβ-1,6-glucan and mannoproteins, linked to the inner layer via chitin andβ-1,3-glucan.

In C. albicans, 50-70% of the cell wall is composed of β-1,3- andβ-1,6-glucans. Protective antibodies against C. albicans β-1,6-glucanhave been generated in mice [8]. Mice in which anti β-1,6-glucanantibodies were raised by idiotypic vaccination withmannoprotein-depleted C. albicans cells were shown to have someprotection against systemic challenge by C. albicans. Furthermore, micepassively immunised with these anti β-1,6-glucan antibodies demonstrateda raised level of protection against C. albicans.

It is an object of the invention to provide further and bettermonoclonal antibodies for inducing therapeutic immune responses againstinfections, particularly against microbial infections.

DISCLOSURE OF THE INVENTION

β-1,3-glucans are a cell wall component of many microbes but arenaturally poor immunogens. As such, anti-β-1,3-glucan antibodies havenot previously been specifically considered for use in therapy. Asdiscussed above, anti-β-1,6-glucan antibodies are known to provide someprotection against fungal challenge. The present inventors havediscovered that anti-β-1,3-glucan antibodies can be more effectiveagainst fungal challenge than anti-β-1,6-glucan antibodies.

The present invention thus relates to monoclonal antibodies that detectand bind to β-1,3-glucan, hybridoma cell lines producing the antibodies,and methods of using such antibodies for treatment of microbialinfections, particularly against Candida albicans or Aspergillusfumigatis infection. The antibodies of the present invention are notspecific for β-1,6-glucan.

ANTIBODIES OF THE INVENTION

The invention provides monoclonal antibodies that can protect a mammalagainst infection by a microbial pathogen, wherein the pathogen has acell wall containing β-1,3-glucan and β-1,6-glucan, and wherein themonoclonal antibody shows preferential binding to the β-1,3-glucan overthe β-1,6-glucan. The antibodies preferably have microbicidal activity.The invention also provides fragments of these monoclonal antibodies,particularly fragments that retain the antigen-binding activity of theantibodies.

An antibody shows preferential binding to a β-1,3-glucan over aβ-1,6-glucan if, under the same conditions, it binds more strongly (asmeasured, for instance, as optical density (OD) readings in an indirectELISA test) with a β-1,3-glucan than with a β-1,6-glucan. Differentialreactivity can be determined, for example, by incubating a constantantibody concentration with scalar concentrations of antigen(β-1,3-glucan and β-1,6-glucan). A higher concentration (e.g.≧10×, >100×) of the lower affinity antigen will be required to giveequivalent OD readings.

Alternatively, competitive-inhibition ELISA experiments can be used todetermine differential binding. For example, each antibody is reactedwith cell wall glycans and either β-1,3-glucan or β-1,6-glucan is addedas a soluble-phase competitor. An antibody shows preferential binding toa β-1,3-glucan over a β-1,6-glucan if, for example, the concentration offree β-1,3-glucan required to cause 50% inhibition of antibody bindingto cell wall glycans is >10× lower than the concentration of freeβ-1,6-glucan required to cause 50% inhibition of antibody binding to thesame cell wall glycans.

For C. albicans, the cell wall glycans are preferably ‘GG-zym’ solubleglucan antigens [8]. These are obtained by (i) preparing glucan ghostsby repeated hot alkali-acid extractions of fungal cell walls to givepurified β-1,3- and β-1,6-glucans and (ii) digesting the ghosts withβ-1,3-glucanase for 1 hour at 37° C. The glycans may be immobilised forinhibition testing.

The term ‘monoclonal antibody’ includes any of the various artificialantibodies and antibody-derived proteins which are available e.g. humanantibodies, chimeric antibodies, humanized antibodies, single-domainantibodies, single-chain Fv (scFV) antibodies, monoclonal oligobodies,dimeric or trimeric antibody fragments or constructs, minibodies, orfunctional fragments thereof which bind to the antigen in question.

In a natural antibody molecule, there are two heavy chains and two lightchains. Each heavy chain and each light chain has at its N-terminal enda variable domain. Each variable domain is composed of four frameworkregions (FRs) alternating with three complementarity determining regions(CDRs). The residues in the variable domains are conventionally numberedaccording to a system devised by Kabat et al. [9]. The Kabat residuedesignations do not always correspond directly with the linear numberingof the amino acid residues and the linear amino acid sequence maycontain fewer or additional amino acids than in the strict Kabatnumbering. This may correspond to a shortening of, or insertion into, astructural component, whether framework or CDR, of the basic variabledomain structure.

A preferred antibody of the invention is 2G8 (SEQ ID NOs: 1 and 2). Theheavy chain variable domain of 2G8 (SEQ ID NO: 2) comprises CDRs whichare located at residues 23-30 (CDR-H1, SEQ ID NO: 4), residues 48-55(CDR-H2, SEQ ID NO: 6) and residues 94-102 (CDR-H3, SEQ ID NO: 8). Thelight chain variable domain of 2G8 (SEQ ID NO: 1) comprises CDRs whichare located at residues 27-37 (CDR-L1, SEQ ID NO: 10), residues 55-58(CDR-L2, SEQ ID NO: 12) and residues-94-102 (CDR-L3, SEQ ID NO: 14).

Antibodies having specificity for β-glucan and comprising one or more(e.g. 1; 2, 3, 4, 5 or 6) of the CDRs from 2G8 are also preferred, asare derivatives of 2G8 in which one or more (e.g. 2, 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15) framework residues are substituted with otheramino acids. Fusion proteins comprising 2G8 or derivatives, at the N- ofC-terminus are also useful. The 2G8 CDRs may optionally each contain 1,2, 3 or 4 amino acid substitutions.

Preferably, the heavy chain of the antibodies of the invention comprisesone or more (e.g. 1, 2, or 3) of the CDRs encoded by SEQ ID NOs 3, 5 and7. Preferably, the light chain of the antibodies of the inventioncomprises one or more (e.g. 1, 2, or 3) of the CDRs encoded by SEQ IDNOs 9, 11 and 13.

Antibody 2G8 is derived from a mouse. To avoid a non-specific anti-mouseimmune response in humans, the antibodies of the invention arepreferably humanized or chimeric. [e.g. refs. 10 & 11]. As analternative, fully-human antibodies may be used.

In chimeric antibodies, non-human constant regions are substituted byhuman constant regions but variable regions remain non-human. Humanizedantibodies may be achieved by a variety of methods including, forexample: (1) grafting complementarity determining regions (CDRs) fromthe non-human variable region onto a human framework (“CDR-grafting”),with the optional additional transfer of one or more framework residuesfrom the non-human antibody (“humanizing”); (2) transplanting entirenon-human variable domains, but “cloaking” them with a human-likesurface by replacement of surface residues (“veneering”). In the presentinvention, humanized antibodies include those obtained by CDR-grafting,humanizing, and veneering of the variable regions. [e.g. refs. 12 to18].

Humanized or fully-human antibodies can also be produced usingtransgenic animals that are engineered to contain human immunoglobulinloci. For example, ref. 19 discloses transgenic animals having a humanIg locus wherein the animals do not produce functional endogenousimmunoglobulins due to the inactivation of endogenous heavy and lightchain loci. Ref. 20 also discloses transgenic non-primate mammalianhosts capable of mounting an immune response to an immunogen, whereinthe antibodies have primate constant and/or variable regions, andwherein the endogenous immunoglobulin-encoding loci are substituted orinactivated. Ref. 21 discloses the use of the Cre/Lox system to modifythe immunoglobulin locus in a mammal, such as to replace all or aportion of the constant or variable region to form a modified antibodymolecule. Ref. 22 discloses non-human mammalian hosts having inactivatedendogenous Ig loci and functional human Ig loci. Ref. 23 disclosesmethods of making transgenic mice in which the mice lack endogenousheavy chains, and express an exogenous immunoglobulin locus comprisingone or more xenogeneic constant regions.

Antibodies naturally have two separate chains, however, it is preferredto use a single chain antibody (“sFv”) in which the light and heavychain variable domains are joined by a linker to give a singlepolypeptide chain. Kits for preparing scFv's are availableoff-the-shelf, and anti-ligand scFvs are preferred second sequences foruse with the invention. Single domain antibodies can also be obtainedfrom camelids or sharks [24], or by camelisation [25].

A sFv polypeptide is a covalently linked V_(H)-V_(L) heterodimer whichis expressed from a gene fusion including V_(H)- and V_(L)-encodinggenes linked by a peptide-encoding linker [26]. A number of methods havebeen described to discern and develop chemical structures (linkers) forconverting the naturally aggregated, but chemically separated, light andheavy polypeptide chains from an antibody V region into an sFv moleculewhich will fold into a three dimensional structure substantially similarto the structure of an antigen-binding site. See, e.g., references 27 to29. The sFv molecules may be produced using methods described in theart. Design criteria include determining the appropriate length to spanthe distance between the C-terminus of one chain and the N-terminus ofthe other, wherein the linker is generally formed from small hydrophilicamino acid residues that do not coil or form secondary structures. Suchmethods have been described in the art [e.g. refs. 27-29]. Suitablelinkers generally comprise polypeptide chains of alternating sets ofglycine and serine residues, and may include glutamic acid and lysineresidues inserted to enhance solubility.

“Mini-antibodies” or “minibodies” will also find use with the presentinvention. Minibodies are sFv polypeptide chains which includeoligomerization domains at their C-termini, separated from the sFv by ahinge region [30]. The oligomerization domain comprises self-associatingα-helices, e.g., leucine zippers, that can be further stabilized byadditional disulfide bonds. The oligomerization domain is designed to becompatible with vectorial folding across a membrane, a process thoughtto facilitate in vivo folding of the polypeptide into a functionalbinding protein. Generally, minibodies are produced using recombinantmethods well known in the art. See, e.g references 30 & 31.

“Oligobodies” will also find use with the present invention. Oligobodiesare synthetic antibodies. The specificity of these reagents has beendemonstrated by Western blot analysis and immunohistochemistry. Theyhave some desirable properties, namely that as their production isindependent of the immune system, they can be prepared in a few days andthere is no need for a purified target protein [32]. Oligobodies areproduced using recombinant methods well known in the art [33].

Antibodies of the invention are preferably neutralising antibodies i.e.they can neutralise the ability of a pathogen (e.g. of C. albicans) toinitiate and/or perpetuate an infection in a host. The antibody canpreferably neutralise at a concentration of 10⁻⁹ M or lower (e.g. 10⁻¹⁰M, 10⁻¹¹ M, 10⁻¹² M or lower).

Antibodies are produced using techniques well known to those of skill inthe art [e.g. refs. 34-39]. Monoclonal antibodies are generally preparedusing the method of Kohler & Milstein (1975) [40], or a modificationthereof. Typically, a mouse or rat is immunized as described above.Rabbits may also be used. However, rather than bleeding the animal toextract serum, the spleen (and optionally several large lymph nodes) isremoved and dissociated into single cells. If desired, the spleen cellsmay be screened (after removal of non-specifically adherent cells) byapplying a cell suspension to a plate or well coated with the antigen.B-cells, expressing membrane-bound immunoglobulin specific for theantigen, will bind to the plate, and are not rinsed away with the restof the suspension. Resulting B-cells, or all dissociated spleen cells,are then induced to fuse with myeloma cells to form hybridomas, and arecultured in a selective medium (e.g., hypoxanthine aminopterin thymidinemedium, ‘HAT’). The resulting hybridomas are plated by limitingdilution, and are assayed for the production of antibodies which bindspecifically to the immunizing antigen (and which do not bind tounrelated antigens). The selected monoclonal antibody-secretinghybridomas are then cultured either in vitro (e.g., in tissue culturebottles or hollow fiber reactors), or in vivo (e.g., as ascites inmice).

The invention also provides a hybridoma expressing the antibody of theinvention. This hybridoma can be used in various ways e.g. as a sourceof monoclonal antibodies or as a source of nucleic acid (DNA or mRNA)encoding the monoclonal antibody of the invention for the cloning ofantibody genes for subsequent recombinant expression.

Antibodies of the invention may be produced by any suitable means (e.gby recombinant expression). Expression from recombinant sources is morecommon for pharmaceutical purposes than expression from B cells orhybridomas e.g. for reasons of stability, reproducibility, culture ease,etc.

The invention provides a method for preparing one or more nucleic acidmolecules (e.g. heavy and light chain genes) that encodes an antibody ofinterest, comprising the steps of: (i) preparing a hybridoma expressingthe antibody of the invention as described above; (ii) obtaining fromthe hybridoma nucleic acid that encodes the antibody of interest. Theinvention also provides a method for obtaining a nucleic acid sequencethat encodes an antibody of interest, comprising the steps of: (i)preparing a hybridoma according to the invention; (ii) sequencingnucleic acid from the hybridoma that encodes the antibody of the presentinvention.

Thus the invention also provides a method for preparing a recombinantcell, comprising the steps of: (i) preparing a hybridoma expressing theantibody of the invention as described above; (ii) obtaining one or morenucleic acids (e.g. heavy and/or light chain genes) from the hybridoma;(iii) inserting the nucleic acid into an expression vector; and (iv)transforming an expression host with the expression vector in order topermit expression of the antibody of interest in that host.

Similarly, the invention also provides a method for preparing arecombinant cell, comprising the steps of: (i) preparing a hybridomaexpressing the antibody of the invention as described above; (ii)sequencing nucleic acid(s) from the hybridoma that encodes the antibodyof interest; (iii) using the sequence information from step (ii) toprepare nucleic acid(s) for inserting into an expression vector; and(iv) transforming an expression host with the expression vector in orderto permit expression of the antibody of interest in that host.

A single expression vector may be constructed which contains the nucleicacid sequences coding for more than one of the antibody chains. Forinstance, the nucleic acid sequences encoding the heavy and light chainsmay be inserted at different positions on the same expression vector.Alternatively, the nucleic sequence coding for each chain, may beinserted individually into an expression vector, thus producing a numberof constructed expression vectors, each coding for a particular chain.Preferably, the expression vectors into which the sequences are insertedare compatible.

The transformed cells of the invention can then be used for expressionand culture purposes. They are particularly useful for expression ofantibodies for large-scale pharmaceutical production. They can also beused as the active ingredient of a pharmaceutical composition. Anysuitable culture techniques can be used, including but not limited tostatic culture, roller bottle culture, ascites fluid, hollow-fiber typebioreactor cartridge, modular minifermenter, stirred tank, microcarrierculture, ceramic core perfusion, etc.

Methods for obtaining and sequencing immunoglobulin genes fromhybridomas are well known in the art e.g. see chapter 4 of ref. 41.

The expression host is preferably a eukaryotic cell, including yeast andanimal cells, particularly mammalian cells (e.g. CHO cells, human cellssuch as PER.C6 (Crucell [42]) or HKB-11 (Bayer; [43,44]) cells, myelomacells [45,46], etc.), as well as plant cells. Preferred expression hostscan glycosylate the antibody of the invention, particularly withcarbohydrate structures that are not themselves immunogenic in humans.Expression hosts that can grow in serum-free media are preferred.Expression hosts that can grow in culture without the presence ofanimal-derived products are preferred.

The expression host may be cultured to give a cell line.

Antibody fragments which retain the ability to recognise a β-1,3-glucanantigen are also included within the scope of the invention. A number ofantibody fragments are known in the art which comprise antigen-bindingsites capable of exhibiting immunological binding properties of anintact antibody molecule. For example, functional antibody fragments canbe produced by cleaving a constant region, not responsible for antigenbinding, from the antibody molecule, using e.g., pepsin, to produceF(ab′)₂ fragments. These fragments will contain two antigen bindingsites, but lack a portion of the constant region from each of the heavychains. Similarly, if desired, Fab fragments, comprising a singleantigen binding site, can be produced, e.g., by digestion of monoclonalantibodies with papain. Functional fragments, including only thevariable regions of the heavy and light chains, can also be produced,using standard techniques such as recombinant production or preferentialproteolytic cleavage of immunoglobulin molecules. These fragments areknown as Fv. See, e.g., references 47 to 49.

Non-conventional means can also be used to generate and identify theantibodies of the invention. For example, a phage display library can bescreened for antibodies of the invention [50-53].

Monoclonal antibodies are particularly useful in identification andpurification of the individual polypeptides or other antigens againstwhich they are directed. The monoclonal antibodies of the invention haveadditional utility in that they may be employed as reagents inimmunoassays, radioimmunoassays (RIA) or enzyme-linked immunosorbentassays (ELISA). In these applications, the antibodies can be labelledwith an analytically-detectable reagent such as a radioisotope, afluorescent molecule or an enzyme. For example, the monoclonalantibodies of the invention may be used to detect circulating β-1-3glucan in patients suffering from candidiasis or aspergillosis [54].

Antibodies of the invention can be coupled to a drug for delivery to atreatment site or coupled to a detectable label to facilitate imaging ofa site comprising cells of interest, such as cancer cells. Methods forcoupling antibodies to drugs and detectable labels are well known in theart, as are methods for imaging using detectable labels.

Antibodies of the invention may be attached to a solid support.

Antibodies of the invention can be of isotype IgA or, preferably, IgG,i.e. an α or γ heavy chain. Within the IgG isotype, antibodies may beIgG1, IgG2, IgG3 or IgG4 subclass. Antibodies of the invention may havea κ or a λ light chain.

Microbicidal Activity

The monoclonal antibody of the invention preferably has microbicidalactivity.

Preferably, it has anti-mycotic activity and/or anti-bacterial activity.Anti-bacterial activity may be against a Gram-negative or Gram-positivebacterium.

More preferably, it has activity against a microbe which has aglucan-based cell wall.

More preferably, it has activity against a microbe which comprises aβ-1,3-linked oligosaccharide cell wall.

Most preferably, it has activity against Candida albicans and/or againstAspergillus fumigatis.

Pharmaceutical Compositions

The use of monoclonal antibodies as the active ingredient ofpharmaceuticals is now widespread, including the products Herceptin™(trastuzumab), Rituxan™, Campath™, Remicade™, ReoPro™, Mylotarg™,Zevalin™, Omalizumab, Synagis™ (Palivizumab), Zenapax™ (daclizumab),etc. These include antibodies that recognise human self-antigens (e.g.Herceptin™ recognises the Her2 marker) and antibodies that recogniseantigens from pathogens (e.g. Synagis™ recognises an antigen fromrespiratory syncytial virus).

The invention provides a pharmaceutical composition comprising (1)monoclonal antibody of the invention and (2) a pharmaceuticallyacceptable carrier.

The invention provides a method of preparing a pharmaceutical,comprising the steps of: (i) preparing a monoclonal antibody of theinvention; and (ii) admixing the purified antibody with one or morepharmaceutically-acceptable carriers.

The composition is preferably substantially free from antibodies whichinhibit the protective efficacy of the anti-glucan antibodies. Forexample, where the glucan is a fungal β-1,3-glucan then the compositionis preferably substantially free from antibodies against non-glucan cellwall components, such as anti-mannoprotein antibodies.

Component (1) is the active ingredient in the composition, and this ispresent at a therapeutically effective amount i.e. an amount sufficientto inhibit microbial/viral growth and/or survival in a patient, andpreferably an amount sufficient to eliminate microbial infection. Theprecise effective amount for a given patient will depend upon their sizeand health, the nature and extent of infection, and the composition orcombination of compositions selected for administration. The effectiveamount can be determined by routine experimentation and is within thejudgement of the clinician. For purposes of the present invention, aneffective dose will generally be from about 0.01 mg/kg to about 5 mg/kg,or about 0.01 mg/kg to about 50 mg/kg or about 0.05 mg/kg to about 10mg/kg of the compositions of the present invention in the individual towhich it is administered. Known antibody pharmaceuticals provideguidance in this respect e.g. Herceptin™ is administered by intravenousinfusion of a 21 mg/ml solution, with an initial loading dose of 4 mg/kgbody weight and a weekly maintenance dose of 2 mg/kg body weight;Rituxan™ is administered weekly at 375 mg/m²; etc. Pharmaceuticalcompositions based on polypeptides, antibodies and nucleic acids arewell known in the art. Polypeptides may be included in the compositionin the form of salts and/or esters.

Carrier (2) can be any substance that does not itself induce theproduction of antibodies harmful to the patient receiving thecomposition, and which can be administered without undue toxicity.Suitable carriers can be large, slowly metabolised macromolecules suchas proteins, polysaccharides, polylactic acids, polyglycolic acids,polymeric amino acids, amino acid copolymers, and inactive virusparticles. Such carriers are well known to those of ordinary skill inthe art. Pharmaceutically acceptable carriers can include liquids suchas water, saline, glycerol and ethanol. Auxiliary substances, such aswetting or emulsifying agents, pH buffering substances, and the like,can also be present in such vehicles. Liposomes are suitable carriers. Athorough discussion of pharmaceutical carriers is available in ref. 55.

Pharmaceutical compositions of the invention ray also be usedprophylactically e.g. in a situation where contact with microbes isexpected and where establishment of infection is to be prevented. Forinstance, the composition may be administered prior to surgery.

In compositions of the invention that include antibodies of theinvention, the antibodies preferably make up at least 50% by weight(e.g. 60%, 70%, 80%, 90%, 95%, 97%, 98%, 99% or more) of the totalprotein in the composition. The antibodies are thus in purified form.

Microbial infections affect various areas of the body and so thecompositions of the invention may be prepared in various forms. Forexample, the compositions may be prepared as injectables, either asliquid solutions or suspensions. Solid forms suitable for solution in,or suspension in, liquid vehicles prior to injection can also beprepared (e.g. a lyophilised composition, like Synagis™ and Herceptin™,for reconstitution with sterile water containing a preservative). Thecomposition may be prepared for topical administration e.g. as anointment, cream or powder. The composition be prepared for oraladministration e.g. as a tablet or capsule, or as a syrup (optionallyflavoured). The composition may be prepared for pulmonary administratione.g. as an inhaler, using a fine powder or a spray. The composition maybe prepared as a suppository or pessary. The composition may be preparedfor nasal, aural or ocular administration e.g. as drops, as a spray, oras a powder [e.g. 56]. The composition may be included in a mouthwash.The composition may be lyophilised.

The pharmaceutical composition is preferably sterile. It is preferablypyrogen-free. It is preferably buffered e.g. at between pH 6 and pH 8,generally around pH 7. Preferably, the composition is substantiallyisotonic with humans.

The invention also provides a delivery device containing apharmaceutical composition of the invention. The device may be, forexample, a syringe or an inhaler.

Compositions of the invention may be used in conjunction with knownanti-fungals. Suitable anti-fungals include, but are not limited to,azoles (e.g. fluconazole, itraconazole), polyenes (e.g. amphotericin B),flucytosine, and squalene epoxidase inhibitors (e.g. terbinafine) [seealso ref 57]. Compositions may also be used in conjunction with knownantivirals e.g. HIV protease inhibitors, a 2′,3′-dideoxynucleoside (e.g.DDC, DDI), 3′-azido-2′,3′-dideoxynucleosides (AZT),3′-fluoro-2′,3′-dideoxynucleosides (FLT),2′,3′-didehydro-2′,3′-dideoxynucleosides (e.g. D4C, D4T) and carbocyclicderivatives thereof (e.g. carbovir),2′-fluoro-ara-2′,3′-dideoxynucleosides, 1,3-dioxolane derivatives (e.g.2′,3′-dideoxyl-3′-thiacytidine), oxetanocin analogues and carbocyclicderivatives thereof (e.g. cyclobut-G) and the9-(2-phosphonylmethoxyethyl)adenine (PMEA) and9-(3-fluoro-2-phosphonylmethoxypropyl)adenine (FPMPA) derivatives,tetrahydro-imidazo[4,5,1-jk][1,4]-benzodiazepin-2(1H)one (TIBO),1-[(2-hydroxyethoxy)-methyl]-6-(phenylthio)thymine (HEPT),dipyrido[3,2-b:2′,3′-e]-[1,4]diazepin-6-one (nevirapine) andpyridin-2(1H)one derivatives, 3TC, etc.

Medical Treatments and Uses

The antibody is a protective, offering protection against microbialinfection and/or disease.

Thus, the invention provides a monoclonal antibody of the invention foruse as a medicament. The invention also provides a method for protectinga patient from a microbial infection, comprising administering to thepatient a pharmaceutical composition of the invention. The inventionalso provides the use of monoclonal antibody of the invention in themanufacture of a medicament for the prevention of microbial infectionand/or disease.

As well as being used in preventative methods, the antibody can also beused to treat an existing microbial infection and/or disease.

Thus, the invention also provides a method for treating a patientsuffering from a microbial infection, comprising administering to thepatient a pharmaceutical composition of the invention. The inventionalso provides the use of monoclonal antibody of the invention in themanufacture of a medicament for treating a patient.

The microbe may be a fungus or a bacterium, examples of which are givenbelow.

The patient is preferably a human, particularly a female. The human maybe an adult or a child.

The antibodies of the invention are particularly useful for treatingmicrobial infections in patients who are: pregnant;immunocompromised/immunosuppressed (T-cell deficient); or undergoingantibiotic therapy or chemotherapy. The antibodies of the invention arealso useful for treating microbial infection in patients who have:systemic microbial infection; indwelling intravascular catheters; HIV;AIDS; neutropenia; previous fungal colonisation; diabetes; leukaemia;lymphoma; burns; maceration; oral cavity infections and patients whohave had prior hemodialysis or who have undergone organ transplants.

These uses and methods are particularly useful for treating infectionsof: Candida species, such as C. albicans; Cryptococcus species, such asC. neoformans; Enterococcus species, such as E. faecalis; Streptococcusspecies, such as S. pneumoniae, S. mutans, S. agalactiae and S.pyogenes; Leishmania species, such as L. major and L. infantum; A.canthamoeba species, such as A. castellani; Aspergillus species, such asA. fumigatus and A. flavus; Pneumocystis species, such as P. carinii;Mycobacterium species, such as M. tuberculosis; Pseudomonas species,such as P. aeruginosa; Staphylococcus species, such as S. aureus;Salmonella species, such as S. typhimurium; Coccidioides species such asC. immitis; Trichophyton species such as T. verrucosum; Blastomycesspecies such as B. dermatidis; Histoplasma species such as H.capsulatum; Paracoccidioides species such as P. brasiliensis; Pythiumnspecies such as P. insidiosum; and Escherichia species, such as E. coli.

The uses and methods are particularly useful for treating diseasesincluding, but not limited to: candidosis, aspergillosis,cryptococcosis, dermatomycoses, sporothrychosis and other subcutaneousmycoses, blastomycosis, histoplasmosis, coccidiomycosis,paracoccidiomycosis, pneumocystosis, thrusb, tuberculosis,mycobacteriosis, respiratory infections, scarlet fever, pneumonia,impetigo, rheumatic fever, sepsis, septicaemia, cutaneous and visceralleishmaniasis, corneal acanthamoebiasis, keratitis, cystic fibrosis,typhoid fever, gastroenteritis and hemolytic-uremic syndrome. Anti-C.albicans activity is particularly useful for treating infections in AIDSpatients.

Efficacy of treatment can be tested by monitoring microbial infectionafter administration of the pharmaceutical composition of the invention.

Compositions of the invention will generally be administered directly toa patient. Direct delivery may be accomplished by parenteral injection(e.g. subcutaneously, intraperitoneally, intravenously, intramuscularly,or to the interstitial space of a tissue), or by rectal, oral, vaginal,topical, transdermal patch, ocular, nasal, aural, or pulmonaryadministration. Injection or intranasal administration is preferred. Itwill be appreciated that the active ingredient in the composition willbe an antibody molecule. As such, it will be susceptible to degradationin the gastrointestinal tract. Thus, if the composition is to beadministered by a route using the gastrointestinal tract, thecomposition will need to contain agents which protect the antibody fromdegradation but which release the antibody once it has been absorbedfrom the gastrointestinal tract.

Dosage treatment can be a single dose schedule or a multiple doseschedule.

As an alternative to delivering monoclonal antibodies for therapeuticpurposes, it is possible to deliver nucleic acid (typically DNA) to asubject that encodes the monoclonal antibody (or active fragmentthereof) of interest, such that the nucleic acid can be expressed in thesubject in situ to provide a desired therapeutic effect. Suitable genetherapy and nucleic acid delivery vectors are known in the art

General

The term “comprising” encompasses “including” as well as “consisting”e.g. a composition “comprising” X may consist exclusively of X or mayinclude something additional e.g. X+Y.

The word “substantially” does not exclude “completely” e.g. acomposition which is “substantially free” from Y may be completely freefrom Y. Where necessary, the word “substantially” may be omitted fromthe definition of the invention.

The term “about” in relation to a numerical value x means, for example,x±10%.

Where the invention refers to antibodies that have two chains (heavy andlight), the invention also encompasses where appropriate the individualchains separately from each other.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the results of an inhibition ELISA test using putativecompetitor ligands against IgG 2G8 and IgM 1E12 mAbs. Percent inhibitionvalues are shown for each putative inhibitor at the four doses tested,and the graph refers to one representative experiment of two withsimilar results.

FIG. 2 shows the results of an inhibition ELISA test using chemicallydefined β-1,3 and β-1,6 standards. Values in the graph are ranges ofpercent inhibition measured for each inhibitor at the three dosestested, and refer to a representative experiment out of two performedwith similar results.

FIG. 3 shows the results of experiments to determine the binding of IgGmAb 2G8 and IgM control mAb to distinct, plastic-adsorbed glucanantigens.

FIG. 4 shows the results of experiments to determine the inhibition ofmAb binding to GG-Zym by β-glucan compounds with distinct molecularstructures. The y-axes shows % inhibition of ELISA reactivity. Thex-axes show the concentration of free inhibitor (mg/ml). Open circlesshow IgM control mAb; closed circles show 2G8 IgG mAb. The free-phaseinhibitors are: (A) laminarin; (B) pustulin; and (C) β-glucan from S.cerevisiae.

FIG. 5 shows the results of experiments to determine the ability by IgGand the IgM mAb to compete for binding to the same antigen. The y-axesshows binding to plastic-adsorbed antigen (OD 405 nm). The x-axes showthe concentration of the competitor mAb (ng/ml). Open circles show thebinding of the IgM control mAb in the presence of mAb 2G8; closedcircles show the binding of 2G8 IgG mAb in the presence of IgM controlmAb.

FIG. 6 shows the indirect immunofluorescence localisation of 2G8 and anIgM control glucan epitopes on C. albicans cell. The Figure representsthe pattern of reactivity observed for the 2G8 and control mAbs in twoindependent experiments. Inserts in panels a and b show thephase-contrast aspect of the same microscopic field of the correspondingpanel. Inserts in panels c, d, e, f, g, h, show details of theimmunofluorescence staining patterns. Magnification, ×1000.

FIG. 7 shows the fungal burden in the kidney of CD2F1 mice followingi.p. administration of 2G8 and IgM control mAbs in a murine experimentalmodel of disseminated candidiasis.

FIG. 8 shows the percent survival at the indicated times of miceadministered a single dose of β-glucan mAbs following a lethal i.v.challenge with C. albicans.

FIG. 9 shows indirect immunofluorescence staining of: (a,d) isolated C.albicans β-glucan cell wall ghosts; (b,e) C. albicans germ-tubes; (c,f)hyphal filaments of C. albicans; (g) germinated conidium of A.fumigatus; (h,i) A. fumigatus hyphae.

FIG. 10 shows CFU numbers after growth of C. albicans in the presence ofserum raised against: (white) adjuvant alone; (grey) CRM carrier alone;or (black) laminarin.

FIG. 11 shows CFU reduction after growth with 0.25, 0.1 or 0.05 mg/ml of(white) 2G8 or (black) anti-CRM monoclonal antibody.

FIG. 12 shows the effect of anti-Lam-CRM or control anti-CRM serum onthe in vitro growth of A. fumigatus, as evaluated by ³H-glucoseincorporation assays.

FIG. 13 shows the numbers of mice surviving intravenous challenge withA. fumigatus after being immunised wither with the Lam-CRM conjugate orwith CRM.

MODES FOR CARRYING OUT THE INVENTION 1. Hybridoma Generation andMonoclonal Antibody Purification

Two female Balb/c mice (Harlan) were immunized with 15 μgpolysaccharide/mouse (corresponding to 251 protein/mouse) of aglycoconjugate between purified β-glucan preparation from the cell wallof C. albicans and the diphtheria genetic toxoid CRM197 (GG-Zym Pool1-CRM 197 conjugate; [8]).

The conjugate was administered once subcutaneously, in complete Freund'sadjuvant, and twice intraperitoneally, at weekly intervals, withoutadjuvant. The final boosting dose (5 μg polysaccharide/mouse) was givenintravenously 4 days before the fusion.

Spleen cells of immunized mice were fused at a 1:1 ratio with myelomacells of the murine line X63-Ag8 653 by standard techniques and hybridswere selected according to standard protocols (see also [58]). Culturesupernatants were screened for antibody production by an indirect ELISA[59], using the C. albicans glucan purified extract GG-Zym or standardglucan compounds (laminarin, pustulan) as coating antigens and analkaline phosphatase-conjugate goat, polyvalent anti-mouseimmunoglobulins antibody (Sigma) as the secondary antibody.

Anti-glucan antibody-secreting hybridoma cultures were cloned twice bylimiting dilution and subsequently grown in vitro in RPMI 1640 (Hyclone)supplemented with 10% fetal calf serum (Hyclone), 100 U penicillin/ml,100 μg streptomycin/ml, 1 mM sodium pyruvate and 2 mM L-glutamine(Hyclone).

A number of stable hybridoma were obtained through this procedure.Monoclonal antibodies (mAb) produced by them could be purified fromculture supernatants by ammonium sulphate precipitation followed bycentrifugation and extensive dialysis of the precipitate against PBS.Purity of precipitated mAbs was evaluated by SDS-PAGE followed byCoomassie blue staining. Titers of mAb preparations were determined byindirect ELISA against the different glucan antigens and defined as thehighest dilution of the antibody giving at least twice the absorbancevalues obtained for the negative control (buffer only).

2. Determination of the Immunoglobulin Class and Isotype

One hybridoma of interest was designated ‘2G8’. It was attributed to theIgG class according to its SDS-PAGE profile and reactivity in ELISA andwestern blot assays with affinity isolated, alkalinephosphatase-conjugated goat anti-mouse? chain antibodies (Sigma). ELISAreactivity with affinity purified, biotin-conjugated anti-mouse IgG1,IgG2a, IgG2b or IgG3 monoclonal antibodies (BD-Pharmingen) indicatedthat the IgG mAb 2G8 belonged to the IgG2b isotype. A second antibody(1E12) was similarly attributed to the IgM class. 1E12 served as acontrol in later experiments.

3. Sequencing of the Monoclonal Antibody Variable Regions

The sequences of the VL and VH regions of 2G8 antibody and of thecontrol IgM antibody were determined. Each V region contains three CDRsindicated as CDR1, CDR2 and CDR3 in one framework region. mRNA wasextracted from the hybridoma cells expressing 2G8 and control IgM andthe corresponding cDNA was synthesised through amplification GAP-DHgene. The VL and VH genes were amplified and products were extracted byagarose gel electrophoresis. The VH and VL regions were then cloned intothe plasmid vector pCR-BluntII-TOPO. The bacterial strain Top 10 wastransformed with the plasmid vector and transformants were analysed. DNAwas then extracted and sequenced.

The sequences of the heavy and light chain variable regions of 2G8 aregiven as SEQ IN NO:1 and SEQ ID NO:2. The CDRs within these sequencesare given as SEQ ID NO:3, SEQ ID NO:5, SEQ ID NO:7, SEQ ID NO:9, SEQ IDNO:11 and SEQ ID NO:13. The same variable region sequences were found inthe 1E12 IgM.

4. Specificity of IgG mAb 2G8 and IgM Control mAb

To investigate the nature of the epitopes preferred by mAbs, we devisedan inhibition ELISA test employing the unfractionated GG-Zym antigen asthe solid-phase reagent, and distinct glucan or non-glucan cell wallfractions from C. albicans, or standard glucan compounds, as free-phasemAb ligands in a competition reaction with the GG-Zym antigen. Thisapproach was chosen because of the possible inability of some of theputative mAb ligands to adsorb effectively to the plastic.

Putative inhibitors, at the concentration of 50, 10, 5 and 1 μg/ml wereadded to appropriate mAb dilutions in PBS, and incubated o.n. at roomtemperature. The reacted mixtures were then added to duplicate wellscoated with GG-Zym (50 μg/ml in carbonate buffer). ELISA tests were thenperformed as previously reported [60], using phosphatase-conjugatedanti-mouse IgG and anti-mouse IgM antibody (Sigma) as the secondaryreagents for mAb 2G8 and IgM control antibodies respectively. Percentinhibition by the various free-phase mAb ligands was calculated bycomparing O.D.405 nm from wells containing the putative inhibitors withthe O.D.405 nm from wells without inhibitors (ranging usually from 0.8to 0.65 in the different experiments). Readings from negative controlwells (buffer only) were subtracted from all O.D. values.

As shown in FIG. 1, the use of non-glucan fungal fraction as competitorligands, such as a total mannoprotein (MP) extract from C. albicans, ora preparation of MPs secreted by the fungus, or even a particular cellwall mannan moiety with similar 1 conformation as glucan (β1,2 mannan),only produced a non significant or a very weak inhibition of ligation of2G8 or IgM control mAbs with the GG-Zym fraction. This also occurredwhen cellopentaose, a non-β-glucan compound, was used as the competitorligand. This indicates that neither a β conformation, nor the merepresence of a sequence of glucose residues were per se sufficient formAb recognition and ligation.

Conversely, a substantial inhibition of the reactivity of both mAbs wasobserved when the GG-Zym fraction (0-65 and 10-87 percent inhibition formAb 2G8 and IgM control mAb, respectively, when used at theconcentration of 1 or 50 μg/ml) was used as an inhibitor, and a nearlycomplete inhibition by a commercial β-glucan preparation from the yeastSaccharomyces cerevisiae (64-90 and 91-100 percent inhibition for mAb2G8 and IgM control mAb, respectively when used at 1 or 50 μg/ml). Acommercial, non-fungal preparation of β-glucan (barley β-glucan) wasalmost totally ineffective as competitor ligand for both mAbs.

Overall, these results indicated that mAb 2G8 and the IgM control mAbrecognised epitopes that are specifically contained in β-glucanextracts. The total MP fraction from C. albicans, which exert a weakinhibitory effect on mAb reactivity, has been reported to contain asmall amount of β-glucan [61]. In addition, mAb specificity is notrestricted to β-glucan from C. albicans, the source of the immunisingantigen, but to be extended to glucans from other yeast species,according to the known structural homogeneity of fungal glucans. Thishas implications for the control of many other fungal pathogens thatexpress critical β-glucan molecules in their cell wall (see below).

5. Chemical Nature of the Epitopes Recognised by 2G8 and IgM Control mAb

The same ELISA inhibition test described above was used to define moreprecisely the chemical nature of mAb epitopes, by the use of chemicallydefined standard β-1,3 and β-1,6 glucans. In particular, laminarin(Sigma), a well characterised preparation from Laminaria digitata, whichis mostly composed by β-1,3-linked glucose residues with few, shortβ-1,6-linked side chains, and a series of linear β-1,3-linked,laminarioligosaccharides with different degree of polymerisation (two toseven) were used. Pustulan (CalbioChem), a standard linear β-1,6-linkedglucan from Umbilicaria papullosa and gentiobiose (β-D-Glc-(1,6)-D-Glc)was also assayed. Two subfractions separated by gel filtration from theGG-Zym antigen, GG-Zym Pool 1 and GG-Zym Pool 2, were also included inthe experiments.

Appropriate mAb dilutions were reacted overnight with inhibitors at 50,10 or 5 μg/ml and then added to duplicate wells coated with GG-Zym.ELISA tests were then carried out, using phosphatase-conjugatedanti-mouse IgG and anti-mouse IgM antibody (Sigma) as the secondaryreagents for mAb 2G8 and IgM control mAb, respectively. Percentinhibition by the various free-phase mAb ligands was calculated asbefore.

Results from a typical ELISA inhibition test performed with thesematerials are shown in FIG. 2.

In these experiments, the two mAbs demonstrated a distinctive bindingpreferences towards laminarin and pustulan. In fact, reactivity of mAb2G8 was almost totally abolished by preincubation with laminarin (38 and89 percent inhibition by 5 and 50 μg/ml, respectively) but not at all bypustulan. On the contrary, pustulan, but not laminarin, was apreferential ligand for the IgM control mAb (24 and 90 percentinhibition at 5 and 50 μg/ml, respectively).

Therefore, it was concluded that mAb 2G8 had a binding preference forglucan in β-1,3 configuration. whereas the control IgM mAb demonstrateda binding preference for glucan in β-1,6 conformation. Preferentialbinding of mAb 2G8 to β-1,3 glucan was confirmed by the observation thatchemically defined β-1,3-linked oligosaccharides (DP of 4 to 7) couldalso efficiently compete for mAb 2G8 ligation, whereas they are notrecognised by the IgM mAbcontrol. However, it was also observed thatoligosaccharides of β-1,3 conformation with lower DP (2 or 3), but notthe β-1,6-linked gentiobiose, could exert a mAb-unspecific, weakinhibitory effect. This suggested that small molecules in β-1,3conformation may be recognised by both mAbs though with a low affinityand specificity.

This latter observation could also contribute to explain the fact thatthe GG-Zym sub-fraction Pool 2 weakly affected reactivity of both mAbs,as this sub-fraction is a mixture of small β-1,3 oligosaccharides with apredominant DP 3 [62]. In contrast, the Pool 1 sub-fraction showed adefinitely higher affinity for the IgM control mAb, in good accordancewith its structure predominantly constituted by β-1,6-linked chains.

6. Binding of IgG mAb 2G8 and IgM Control mAb to Distinct,Plastic-Adsorbed Glucan Antigens

ELISA plates coated with GG-Zym, pustulan or laminarin were reacted withdecreasing amounts of 2G8 or control mAb (purified, ammoniumsulphate-precipitated preparations from culture supernatants insynthetic, protein-free medium) and developed with specific, anti mouseIgM or IgG, AP-conjugated secondary antibodies followed by the enzymesubstrate. FIG. 3 shows O.D. 405 nm absorbance readings generated by themAbs reacting with distinct glucan antigens, as indicated.

As shown in FIG. 3, the 2G8 and the control mAbs exhibited differentaffinities towards glucan molecules of different molecular conformation.In particular, the IgM control mAb preferentially binds β(1-6) glucan,compared to the IgG mAb 2G8. Approximately 3.0 ng/ml of IgM control mAbgenerated an O.D.405 nm value of 0.5, upon reaction with pustulan,whereas at least 100 ng/ml of the IgG 2G8 mAb were required to obtainthe same O.D. reading. Furthermore, the IgG 2G8 mAb preferentially bindsthe β(1-3) glucan, since only 0.04 ng/ml were able to produce an O.D. of1.0 by reacting with laminarin, when compared to approximately 10 ng/mlof IgM mAb required to obtain the same level of biding to this antigen.As a control, the two mAbs were also tested for binding to GG-Zym, aβ(1-6) and β(1-3) glucan-containing preparation from C. albicans and, asexpected, the mAbs showed an overlapping binding curve upon reactionwith this composite glucan fraction containing both conformations.

7. Inhibition of mAb Binding to GG-Zym by β-Glucan Compounds withDistinct Molecular Structures

We further investigated the affinity of the two mAbs for glucanmolecules of different conformation by performing ELISA inhibitionexperiments. Fixed concentrations of mAbs were reacted withplastic-immobilized GG-Zym in the presence of increasing concentrationsof laminarin, pustulan or β-glucan from S. cerevisiae. Ability of thesefree-phase ligands to compete with GG-Zym for mAb binding was evaluatedby comparing the O.D.405 nm readings obtained in the precence of theinhibitors with those measured in the absence of inhibitors. Resultswere expressed as percent inhibition of ELISA reactivity.

The experiments indicated that both mAbs showed a significantly reducedbinding to GG-Zym in the presence of high doses of either pustulan(β-1,6 glucan) or laminarin (β-1,3 glucan), confirming their basicability to recognize glucan antigens of any conformation (FIG. 4). Onthe other hand, on a dose-response basis, the ability of β-1,6 and β-1,3glucans to compete with mAb binding to GG-Zym greatly differed betweenthe IgM and the IgG mAb, as shown by the opposite profile of inhibitioncurves in FIG. 4. In fact, ELISA percent inhibitory dose 50 (ID50), i.e.the doses of competitor ligand producing a 50% reduction of O.D. 405 nmvalues with respect to non-competed mAb readings, were 0.01 and 2.0mg/ml for laminarin and pustulan, respectively, when used tocompetitively bind the IgG mAb, whereas they were 2.0 and 0.05 mg/mlwhen used to competitively bind the control IgM mAb.

8. Ability by IgG and the IgM mAb to Compete for Binding to the SameAntigen

Plastic-bound laminarin or pustulan were reacted with a mixturecontaining a fixed amount of any of the two mAb and decreasingconcentration of its mAb counterpart of different isotype. Binding ofIgG or of IgM mAb was revealed by an appropriate secondary reaction withAP-conjugated anti mouse IgG or IgM antibodies.

FIG. 5 shows the O.D. 405 readings generated by each mAb in the absence(empty symbols) or in the presence (full symbols) of different doses ofcounterpart mAb. The control IgM mAb demonstrated a pronounced abilityto displace the IgG mAb not only upon reaction with pustulan, theantigenic substrate to which it has a greater affinity but even uponreaction with laminarin, an antigen for which it has a reduced affinity.

9. Expression of mAb 2G8 and IgM control mAb Epitopes on C. albicansCells

Untreated, live yeast cells (a, e) or germ-tubes (b, f), yeast cellstreated with dithiothreitol and proteinase K (c, g) and purified glucanghosts from C. albicans were spotted onto microscope slides and reactedwith mAb 2G8 (a, b, c, d) or control IgM mAbs (e, f, g, h). mAb ligationwas revealed with fluorescein isothiocyanate-conjugate anti mouse IgG orIgM antibody (Sigma), and observed with a Leitz Diaplan fluorescencemicroscopy.

Immunofluorescence staining of live, intact yeast or germ-tube cellsdemonstrated that the mAb 2G8 epitope was not expressed on the cellsurface in in vitro cultured Candida cells (FIG. 6, a, b). The surfaceof both yeasts and germ-tube positively reacted with control IgM mAb(FIG. 6, e, f) though not uniformly. Control IgM mAb preferentialepitopes were particularly prominent in specific zones of the yeastcells, apparently corresponding to bud scars, and on emerging buds. Ingerm-tubes, IgM control mAb appeared to stain with a particularintensity the primary septum between mother yeast cell and theprotruding hyphal filament, and particular areas of the hyphal filamentitself (FIG. 6, e, f and relative inserts). The treatment withdithiothreitol and proteinase K, which is known to remove thesuperficial, mannoproteic, cell wall layer, rendered yeast cellsuniformly reactive with control IgM mAb and also exposed some mAb2G8-reactive cell wall components

(FIG. 6, c, g). Both mAbs demonstrated a strong and comparably intensereactivity with purified glucan ghosts, i.e. cells deprived of solubleouter and inner cell wall and cytoplasmic components by strong hotalkali and acid extraction (FIG. 6, d,h).

It can be concluded that mAb 2G8 preferentially recognised constituentsconfined in the inner cell wall layers, whereas control IgM mAbpreferentially recognised epitopes that span the entire cell wall. Thisis consistent with the proposed differential preferences of the mAbs forβ-1,3 and β-1,6 glucan and with the current knowledge on the finestructural organisation of the yeast cell wall [63]. In particular, thefinding that control IgM mAb-preferred, β-1,6 glucan epitopes aresurface expressed is in line with the notion that a β-1,6-linked glucanmoiety is tightly interconnected with the superficial capsule-likemannoprotein layer of Candida cell wall [63].

10. 2G8, but not Control IgM Anti-Glucan mAb can Protect AgainstDisseminated Experimental Candidiasis

It has been suggested that anti β-glucan antibodies may significantlycontribute to the protection against disseminated Candida infectionswhich is induced by vaccination with glucan-exposing Candida cells [59].The anti-glucan mAbs of the present invention were assayed in a murinemodel of disseminated candidiasis.

CD2F1 mice were given a single i.p. administration (0.5 ml) of 2G8 orcontrol IgM purified mAb preparations of equivalent anti-glucan titersand protein content, followed, 2 hours later, by a sublethal i.v.challenge with C. albicans.

In A, groups of three mice were injected i.p. with 0.5 ml of purifiedpreparations of mAb 2G8 or control IgM, or with PBS only (Contr). In B,mice were given 0.25 ml of each mAb diluted with 0.25 ml PBS, or amixture of the two (0.5 ml total). Animals were challenged i.v. 2 hourslater with 5×10⁵ cells of C. albicans.

Two days after challenge, the animals were sacrificed and the fungalburden in the kidney was evaluated by a classical CFU enumeration todetermine protection in comparison with control, PBS-treated mice. Theresults from the three independent experiments are shown in FIG. 7,panel a. Data represent weighted means+SE of CFU counts measured foreach group. The asterisks indicate a statistically significantdifference (*P<0.05 and **P<0.001) with respect to the control group(two-tailed Student's t test).

Despite the well-known and expected variability of these in vivoexperiments, and the use of a single mAb administration, it was foundthat animals receiving mAb 2G8 had significantly fewer fungal cells intheir kidneys than animals receiving control IgM mAb or control animalstreated with buffer only. In one experiment, Candida colonisation of themouse kidney was substantially negated by the mAb treatment.Interestingly, control IgM mAb was completely ineffective in contrastingfungal invasion, as treated mice always showed CFU counts in theirkidneys which were comparable or even higher than those measured in thecontrol group.

In another experiment, the animals received both mAbs, at half strength,and the protective ability was compared with single, half strength mAb(FIG. 7, panel b). Interestingly, the control IgM mAb was not onlyincapable of conferring protection by itself but was also capable ofnegating the protection conferred by the anti beta-1-3 mAb. This is inline with the supposed role of blocking antibodies for some anti-cellsurface specificities as suggested in reference 64.

To further investigate the protective activity exerted by 2G8 mAb,survival of mAb-treated mice following a lethal fungal challenge wasalso monitored. In a preliminary experiment (FIG. 8), mice (7 per group)received i.p the same dose of purified mAbs as in experiments of FIG. 7a, or PBS only (Control). Two hours later, the animals were challengedi.v. with 10⁶ cells of C. albicans. A single i.p. injection of mAb 2G8 2hours before challenge significantly prolonged mice survival, incontrast with the complete lack of protective effect by control IgM mAb.

11. 2G8 Binds to Aspergillus and Candida and Inhibits Fungal Growth

Anti-laminarin serum and the 2G8 mAb were used for immunofluorescencestaining of (i) isolated β-glucan cell wall ghosts of C. albicans; (ii)C. albicans germ tubes; (iii) hyphal filaments of C. albicans; (iv)germinated conidium of A. fumigatus; and (v) A. fumigatus hyphae.Results are shown in FIG. 9. Panels (a), (b), (c), (g) and (h) showresults using the anti-laminarin serum; panels (d), (e), (f) and (i)show results using 2G8. Thus both of the antibody preparations bind toall of the fungal samples.

Moreover, in vitro growth of C. albicans and A. fumigatus issignificantly restricted by the anti-β-glucan antibodies, and Lam-CRMvaccination significantly prolongs the survival of mice subjected to asystemic challenge with A. fumigatus.

FIG. 10A shows the number of CFU in C. albicans cultures grown overnightin the presence of whole or 1:10 diluted anti-Lam-CRM or control sera,and the anti-glucan serum significantly reduces growth compared tocontrols.

FIG. 11 shows the dose-response of C. albicans CFU reduction by the 2G8mAb or by a control anti-CRM mAb. 2G8 shows significantly better CFUreduction at 0.25 and 0.1 mg/ml.

FIG. 12 shows the effect of anti-Lam-CRM and control anti-CRM serum onthe in vitro growth of A. fumigatus, as evaluated by ³H-glucoseincorporation assays.

FIG. 13 shows the numbers of mice surviving intravenous challenge withA. fumigatus after being immunised wither with the Lam-CRM conjugate orwith CRM.

It will be understood that the invention has been described by way ofexample only and modifications may be made whilst remaining within thescope and spirit of the invention.

REFERENCES (THE CONTENTS OF WHICH ARE HEREBY INCORPORATED BY REFERENCE)

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1. A monoclonal antibody that can protect a mammal against infection bya microbial pathogen, wherein the pathogen has a cell wall containingβ-1,3-glucan and β-1,6-glucan, and wherein the monoclonal antibody showspreferential binding to the β-1,3-glucan over the β-1,6-glucan.
 2. Theantibody of claim 1, wherein the antibody comprises one or more CDRshaving an amino acid sequence selected from one or more of SEQ ID NOs:4,6, 8, 10, 12 and
 14. 3. The antibody of claim 1, wherein the antibodyhas a variable domain sequence of SEQ ID NO: 1 and/or SEQ ID NO:2. 4.The antibody of claim 1, wherein the antibody is a human or humanisedantibody or is a chimeric antibody.
 5. The antibody of claim 1 whereinthe antibody is a single chain antibody.
 6. A monoclonal antibodyaccording to claim 1 wherein the antibody has microbicidal activityagainst the microbial pathogen.
 7. A monoclonal antibody according toclaim 6, wherein the microbial pathogen is a: Candida; Cryptococcus;Enterococcus; Streptococcus; Leishmania; Acanthamoeba species;Aspergillus species; Pneumocystis species; Mycobacterium species;Pseudomonas species; Staphylococcus species; Salmonella species;Coccidioides; Trichophyton; Blastomyces; Histoplasma, Paracoccidioides;Pyiumn or Escherichia.
 8. A monoclonal antibody according to claim 7wherein the microbe is C. albicans.
 9. A monoclonal antibody accordingto claim 7 wherein the microbe is A. fumigatis.
 10. (canceled)
 11. Ahybridoma expressing the antibody of claim
 1. 12. Nucleic acid thatencodes the antibody of claim
 1. 13. An expression vector containing thenucleic acid of claim
 12. 14. A host cell transformed with theexpression vector of claim
 12. 15. A pharmaceutical compositioncomprising a monoclonal antibody according to claim 1 and apharmaceutically acceptable carrier.
 16. The composition of claim 15,further comprising an anti-fungal.
 17. A method of protecting a patientagainst microbial infection comprising administering to the patient apharmaceutical composition of claim
 15. 18. (canceled)
 19. The method ofclaim 17, wherein the patient is a: human; female; pregnant;immunocompromised or immunosuppressed; or undergoing antibiotic therapyor chemotherapy; has systemic microbial infection; indwellingintravascular catheters; HIV; AIDS; neutropenia; previous fungalcolonization; diabetes; leukaemia; lymphoma; burns; maceration; oralcavity infections; have had prior hemodialysis or who have undergoneorgan transplants.
 20. The method of claim 17 for protecting against:aspergillosis, cryptococcosis, dermatomycoses, sporothrychosis and othersubcutaneous mycoses, blastomycosis, histoplasmosis, coccidiomycosis,paracoccidiomycosis, pneumocystosis, thrush, tuberculosis,mycobacteriosis, respiratory infections, scarlet fever, pneumonia,impetigo, rheumatic fever, sepsis, septicaemia, cutaneous and visceralleishmaniasis, corneal acanthamoebiasis, keratitis, cystic fibrosis,typhoid fever, gastroenteritis and hemolytic-uremic syndrome.
 21. Themethod of claim 17 for protecting against candidiasis.